1. Field of the Invention
The present invention relates to a sheet feeder and an suitable for the sheet feed in an image forming apparatus such as a copier, a printer, a facsimile apparatus or a composite apparatus.
2. Description of the Related Art
A conventional sheet feeder installed in an image forming apparatus such as a printer is known, for example, from Japanese Unexamined Patent Publication No. H07-144771. The image forming apparatus disclosed in this publication includes left and right main frames forming a housing as a main body of the image forming apparatus, wherein a space into which a sheet cassette is detachably insertable is defined inside the two main frames. Sheets stacked in the sheet cassette are lifted up by a lifting mechanism while being kept stacked, and the upper surface of the uppermost one of the sheets is pressed from below against a pickup roller provided in an apparatus main body, thereby setting a sheet feedable state.
Here, the lifting mechanism is provided in the sheet cassette, whereas a driving unit for driving this lifting mechanism is normally mounted in the apparatus main body. An example of a mounting structure for this driving unit is shown in FIG. 6.
In FIG. 6, right and left main frames 523, 524 are arranged while being spaced apart, wherein one main frame 523 is formed with a space used to install the driving unit. This driving unit includes a motor 520 as a driving source for the lifting mechanism, an input gear 513, and an idle gear train 521 for transmitting a driving force outputted from the motor 520 to the input gear 513, and these are mounted on the outer side of a side wall of the main frame 523. The input gear 513 is mounted at such a position as to be engaged with a gear included in the lifting mechanism provided in the sheet cassette when the sheet cassette is mounted in the apparatus main body by being inserted into the space between the two main frames 523, 524.
Guiding grooves 523a, 524a facing each other are formed in the inner surfaces of bottom parts of both main frames 523, 524. These guiding grooves 523a, 524a extend in an inserting direction of the sheet cassette, along which direction the sheet cassette is guided. The sheet cassette is inserted into the space defined between the two main frames 523, 524 while being guided by the guiding grooves 523a, 524a, and is set at a position where the above input gear 513 can be engaged with the specified gear included in the lifting mechanism provided in the sheet cassette. In this state, a driving force outputted from the motor 520 is transmitted to the gear of the lifting mechanism provided in the sheet cassette via the idle gear train 521 and the input gear 513, thereby actuating the lifting mechanism.
This driving unit is mounted on the outer side of the main frame 523 together with other parts. After the driving unit is mounted, external members such as decorative sheets are arranged at the outer sides of the main frames 523, 524 to cover the driving unit in lateral direction, whereby the assembling of the image forming apparatus is completed.
During the assembling or after completing the assembling of the image forming apparatus, there are cases where the above driving unit needs to be inspected, repaired or exchanged upon the confirmation of a defect in an operation test of the image forming apparatus or during the maintenance after the delivery. For such an inspection or the like of the driving unit, it is necessary to detach the above external members and expose the driving unit to the outside of the apparatus. Further, for the repair or exchange of the driving unit, it is necessary to detach the driving unit from the main frame.
However, the external members are generally large and cannot be easily detached or remounted. Thus, if the external members are detached every time an adjustment or the like of the driving unit is made, it leads to a reduction in operation efficiency.
Further, since the driving unit needs to be connected with the lifting mechanism of the sheet cassette inserted into the above cassette accommodating space, it is frequently located at a side more toward the cassette accommodating space than other parts, i.e. at an inner side when viewed from the outside of the image forming apparatus. In such a case, it is not easy to inspect or detach the driving unit even with the external members detached.